Flexible insulants for containers and conduits

ABSTRACT

AN IMPROVED THERMAL INSULATING MATERIAL FOR SYSTEMS CONTAINING LIQUIFIED GASES AT LOW TEMPERATURES, SAID INSULANT BEING A HYDROCARBON-BASED FOAM HAVING A FREEZING TEMPERATURE LOWER OR SLIGHTLY HIGHER THAN THE LIQUIEFIED GASES.

Aug- 8, N72 1... F. CREASER 3,

FLEXIBLE INSULANTS FOR CONTAINERS AND CONDUITS Filed May 13, 1970 FIG.

INVENTOR:

LEONARD F. CREASER BY:

M M HIS AGENT FIG.

3,682,824 FLEXIBLE INSULANTS FOR CONTAINERS AND CONDUITS Leonard F. Creaser, Wirral, England, assignor to Shell Oil Company, New York, N .Y. Filed May 13, 1970, Ser. No. 36,828

Claims priority, application Great Britain, Nov. 11, 1969,

55,096/ 69 Int. Cl. C04b 43/00; E161 59/14; B65d 81/38 U.S. Cl. 25262 5 Claims ABSTRACT OF THE DISCLOSURE An improved thermal insulating material for systems containing liquefied gases at low temperatures, said insulant being a hydrocarbon-based foam having a freezing temperature lower or slightly higher than the liquefied gases.

This invention relates to thermal insulating materials, and particularly to thermal insulating materials for use in connection with the transport and storage of liquefied gases.

BACKGROUND OF THE INVENTION Many thermal insulating materials, hereinafter referred to as insulants are known in the art for the insulation of vessels, conduits and the like for the storage or transport of substances as described in U.S. Pats. 2,330,966; 3,045,709; 2,940,631; 2,947,438; 2,947,780 or 3,101,861. However, in the storage and transportation of liquefied gases at low temperatures, the problem "becomes complex and in this field of technology, no satisfactory insulants have been found. Contraction of the insulant on cooling from ambient temperature, for example, may cause cracking resulting in the breakdown of the internal structure of the insulant and/or in the separation of the insulant from the wall of the vessel or conduit, with consequent reduction in insulating efiiciency. The use of conventional insulants, such as normally solid cellular materials, sometimes complicates the examination and repair of the insulated vessel or conduit in that, should it be necessary, removal of the insulant may prove difiicult.

In the transport of liquefied gases, particularly liquefied natural gas (LNG), at low temperatures in insulated container ships, the loading and unloading points for such ships is generally done with the aid of insulated flexible conduit, joints, loading arms, etc. Insulated flexible conduit may also be used for the transport of such liquefied gases between storage tanks. It will be apparent that in such devices, where a degree of movement must be expected, the tendency of conventional brittle insulants to crack, and possibly fragment, will be greater than when they are used as insulating material for rigid containers.

Due to the importance of liquefied gases in domestic and commercial applications, the invention will be described with particular reference to these materials. However, the invention is applicable to the insulation of vessels and conduit for other low temperature materials, and where the expression liquefied gases is used hereinafter it is to be understood as referring not only to liquefied natural gas (LNG), but to other materials such as LPG, CO N which may be stored or transported at low temperatures i.e. of the order of 210 K. to 75 K.

SUMMARY OF THE INVENTION It has been found that the reduction or even complete elimination of insulant cracking due to cooling can be accomplished by employing as the insulant a hydrocarbon-based foam which freezes at a temperature lower than, or only slightly higher than that at which the Patented Aug. 8, 1972 liquefied gas is to be stored or transported. According to one aspect of the invention, therefore, there is provided a method of thermally insulating a vessel or conduit adapted to transport and/or store liquefied gas, by means of an insulant which is flexible at ambient temperature and which solidifies at a temperature lower than or slightly above the temperature of the liquefied gas.

Preferably the insulant is one which remains flexible at the storage or transport temperature.

The insulants of the invention are gelled hydrocarbonfoams which can be prepared by judicious choice of certain components so that the foam does not solidify at a temperature so high that further cooling to the temperature of the liquefied gas produces serious cracking. Suitably the foam solidifies at a temperature below or up to 40", preferably 20 K., above that of the liquefied gas.

The selection of the insulant to be employed according to the invention can be made with regard to the temperature of the liquefied gas which is to be transported or stored. Such liquefied gases have a wide range of temperatures (they are usually stored and carried at a temperature about their boiling point at ambient pressure). For example LNG has a temperature of about K.

The insulants of the invention comprise a hydrocarbon component preferably of a lower molecular weight, preferably a gasoline fraction, hydrocarbon having a freezing or setting point approximating to the temperature of the liquefied gas, a gelling agent, and optionally a foaming agent or emulsifier.

The hydrocarbon component can be a mixture of hydrocarbons or substituted hydrocarbons, and due regard should be given in their selection, to the fact that their freezing or setting temperature could be influenced by the presence of other components, for example, the gelling agent, or, if present, the emulsifier.

Generally, the hydrocarbon component comprises one or more normally liquid low molecular weight hydrocarbons having a hydrocarbon chain length of from about 8 to about 16 carbon atoms such as gasoline, about 8 or 9, or kerosene fractions being typical examples of such materials, and containing hydrocarbon components having an average chain length within the stated range. Substituted hydrocarbons, such as hydrocarbons containing substituted halo atoms, or other substituents, may be employed either as the sole hydrocarbon constituent, or part of it, for example to control the freezing point of the insulant or to influence some other characteristic, such as the degree of inflammability.

Gasoline is the preferred hydrocarbon for use as an insulant for LNG according to the invention, since foams made from it maintain their flexibility to LNG temperature. Kerosene foams solidify at about K. so that they are more suitable for the insulation of materials about that temperature.

The foams used according to the invention are of relatively small cell size--1ess than 2 mm., and preferably less than 1 mm., in average diameter and contain from 30 to 90% of gas by volume.

The foams are gelled to assist in the maintenance of their foamed state. Gelling of the foam may be brought about by any suitable gelling agent, any of which are now known from extensive research in connection with the preparation of safety fuels. As a preferred example We may mention aluminum soaps, particularly aluminum octoate. The gelling agent may be employed in any convenient proportion, but we have found that from 2 to 10%, preferably 3 to 7% by weight of the hydrocarbon component is generally satisfactory.

Selection of the gelling agent will of course be made with regard to the nature of the hydrocarbon component t sfisas 'of the insulant, in th'e-Iight'of known'requi'rements" for 'The emulsifier, when used, is employed to facilitateithe produc tion'of afoam. Emulsi fiers are usually unnece sary for the preparation of gasoline and kerosene foarns which are subjected to a gelling step before foaming, or

"which are foamed ,by expulsion of the hydrocarbon through a 'noz'zlewith a pressurized gas, but where they are employed they, should be soluble in the hydrocarbon. Silicone based emulsifiers and condensates of an alkylphenol and an alkylene oxide such as Triton X- -lOO (Rohr'n'and Haas),Triton X 45, etc., aregenerally effec- "tive but the range "of known emulsifiers is wide.

The blowing agent a term which includes gas such 'as inert gases, e.g., nitrogen, CO methane, fluoro-hydrocarbons, etc.', are incorporated in the mixture by agitation, under pressure or by evolution within the'mi'xture (for example, by chemical reaction) mayremain as a gas, orit maybe converted to the liquid or solid state at the'temperature of the liquefied gas which is tobe insulated. Permanentgases, that is, gases which remain in the gaseous'state at the temperature of the' liquefie'd gas to be insulated are preferred. For reasons both of safety and convenience, we prefer to employ an inert gas, parti'c ularly nitrogen, as the blowing agent.

Other blowing agents which may be employed according to the invention include fiuoro-hydrocarbons such'as 'fiuorinated olefins, e.g., Arcton or Freon range of materials having low boiling points and low' surface tension and made by Du Pont under the quoted trade name.

FIG. 1 is a section of a'con'duit 1, supported by supportsv 2 and lying within a trough or trench and surrounded by a foamed insulant composition 3 according to the invention. A cover 4 is shown in position covering the trough.

FIG. 2 is a section of a storage vessel 5 surrounded by a foariiedinsulant 6 according-to the invention and supported by supports7, the whole being bounded by an outer casing 8'through which pass tubes 9 for injecting or removal of the insultant foam.

PREFERRED EMBODIMENT OF INVENTION The invention is illustrated by the following examples.

Example 1 An insulant. suitable forthe insulation of LNG storage vessels and conduits (LNG has a temperature of about 160 C.) was prepared by mixing together 100 gin. gasoline and gm. of aluminum octoate in a pressure vessel and injecting nitrogen gas into the mixture at a pressure of about 35 atmospheres, and agitating the mixture vigorously. The pressure vessel was opened, with ejection of a gelled foam which was used to insulate a vessel containing LNG. The foam, which was flexible at 113 K. had a thermal conductivity of 0.053.B.t.u./ft-. f E/hr.

Example 2 and a gasoline foam 6 and 9 prepared as described in Example 1 was introduced into the .space between the vessel and outer wall via conduit 9'. LNG was poured into the storage vessel'via conduits 10 and 11 and as the foam The invention provides, therefore, a foamed insulant comprising a low molecular weight liquid hydrocarbon,

The insulant, because of its non-rigid nature at'ambient temperature, can be confined within an enclosure surrounding the vessel or conduit to be insulated. The insulant is conveniently introduced into the said enclosure by pouring (where this is feasible), or by pumping" it through suitably disposed nozzles to effect its-. -satisfactory distribution within the enclosure.

The insulant may be introduced into the enclosure by pouring before or after foaming, whichevermethod is most convenient.

The enclosure within which comprise a cavity bounded on the one side by the wall of theavessel or conduit and on the other by an wouter wall, so that'a double walled structure is obtained. Alternatively, the enclosure may comprise a trough or hole in the foam is contained may .the outer casing and the storage vessel to occupy the space left by the cooled foam.

I claim 'as my invention:

1. A process of insulating containers and conduits containing or through which are transported low-tempera- .ture. liquefied materials comprising insulating said concontainers and conduits.

which the vessel or conduit is suspended or placed, the into surliquefied gas or freezes to a rigid foam at a temperature slightly above the temperature of the liquefied gas. DESCRIPTION OF THE maAwl Nos In the accompanying drawing vention.

s, which illustrate the intainers andconduits by applying to the surface of said containersrand conduits .a flexible, crack-resistant insulating gelled foam material obtained by gas blowing with an inert gas a mixture of a hydrocarbon containing from about :8 to about 16- carbon atoms and a gelling agent,

.said gelling agent comprising from about 2 toabout 10% of the mixture and said gelled foamed insulating material thus formed having a freezing point Within the tempera ture, of that of the liquid material being insulated in said 2. A process of insulating pipelines and containers transporting and/or-storing liquefied natural gas comprisingtreating the surfacezof said pipelines and containers .With a nitrogen-blown gelled aluminum soap-gasoline fi A process of insulating pipelines and containers transportingand/or storing- .liquefied natural gas comprising treatingthe surface of said pipelines and containers with a"riitrogen-b'lown gelled aluminum soapkerosene foam.. 4. A process of insulating pipelines and containers transporting and/or. storing liquefied natural gas comprising treating the surface of said pipelines and containerswith a nitrogen-blown gelled aluminum octoate-kerosene foam.

5. A process of insulating pipelines and containers transporting and/ or storing liquefied natural gas comprising treating the surface of said pipelines and containers with a nitrogen-blown gelled aluminum octoate-kerosene foam.

References Cited UNITED STATES PATENTS 6 Saddison 138--34 Ceintry 13 8-146 X Oosterbaan 138-32 X Kilpert et a1. 138--146 X Maybee 138-149 Rollins 138-449 Heller 25262 X Bohland 252316 X 10 HAROLD ANSI-1BR, Primary Examiner US. Cl. X.R. 

